Time course of erythropoietin, triiodothyronine, thyroxine, and thyroid-stimulating hormone at 2,315 m

Effects of altitude on thyroid disorders according to Chinese three-rung, ladder-like topography: national cross-sectional study

BACKGROUND

Chinese topography appears a three-rung ladder-like distribution of decreasing elevation from northwest to southeast, which is divided by two sloping edges. Previous studies have reported that prevalence of thyroid diseases differed by altitude, and geographical factors were associated with thyroid disorders. To explore the association between three-rung ladder-like regions and thyroid disorders according to unique Chinese topographic features, we conducted an epidemiological cross-sectional study from 2015-2017 that covered all 31 mainland Chinese provinces.

METHODS

A total of 78,470 participants aged ≥ 18 years from a nationally representative cross-sectional study were included. Serum thyroid peroxidase antibody, thyroglobulin antibody, and thyroid-stimulating hormone levels; urine iodine concentration; and thyroid volume were measured. The three-rung ladder-like distribution of decreasing elevation from northwest to southeast in China was categorized into three topographic groups according to elevation: first ladder, > 3000 m above sea level; second ladder, descending from 3000-500 m; and third ladder, descending from 500 m to sea level. The third ladder was further divided into groups A (500-100 m) and B (< 100 m). Associations between geographic factors and thyroid disorders were assessed using linear and binary logistic regression analyses.

RESULTS

Participants in the first ladder group were associated with lower thyroid peroxidase (β = -4.69; P = 0.00), thyroglobulin antibody levels (β = -11.08; P = 0.01), and the largest thyroid volume (β = 1.74; P = 0.00), compared with the other groups. The second ladder group was associated with autoimmune thyroiditis (odds ratio = 1.30, 95% confidence interval [1.18-1.43]) and subclinical hypothyroidism (odds ratio = 0.61, 95%confidence interval [0.57-0.66]) (P < 0.05) compared with the first ladder group. Group A (third ladder) (500-100 m) was associated with thyroid nodules and subclinical hypothyroidism (P < 0.05). Furthermore, group B (< 100 m) was positively associated with autoimmune thyroiditis, thyroid peroxidase and thyroglobulin antibody positivity, and negatively associated with overt hypothyroidism, subclinical hypothyroidism, and goiter compared with the first ladder group(P < 0.05).

CONCLUSION

We are the first to investigate the association between different ladder regions and thyroid disorders according to unique Chinese topographic features. The prevalence of thyroid disorders varied among the three-rung ladder-like topography groups in China, with the exception of overt hyperthyroidism.

Exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot environment following 10-day continuous hypoxic exposure

We examined the effects of acclimatization to normobaric hypoxia on aerobic performance and exercise thermoregulatory responses under normoxic, hypoxic, and hot conditions. Twelve men performed tests of maximal oxygen uptake (V̇O2max) in normoxic (NOR), hypoxic [HYP; 13.5% fraction of inspired oxygen (FiO2)], and hot (HE; 35°C, 50% relative humidity) conditions in a randomized manner before and after a 10-day continuous normobaric hypoxic exposure [FiO2 = 13.65 (0.35)%, inspired partial pressure of oxygen = 87 (3) mmHg]. The acclimatization protocol included daily exercise [60 min at 50% hypoxia-specific peak power output (Wpeak)]. All maximal tests were preceded by a steady-state exercise (30 min at 40% Wpeak) to assess the sweating response. Hematological data were assessed from venous blood samples obtained before and after acclimatization. V̇o2max increased by 10.7% ( P = 0.002) and 7.9% ( P = 0.03) from pre-acclimatization to post acclimatization in NOR and HE, respectively, whereas no differences were found in HYP [pre: 39.9 (3.8) vs. post: 39.4 (5.1) ml·kg−1·min−1, P = 1.0]. However, the increase in V̇O2max did not translate into increased Wpeak in either NOR or HE. Maximal heart rate and ventilation remained unchanged following acclimatization. Νo differences were noted in the sweating gain and thresholds independent of the acclimatization or environmental conditions. Hypoxic acclimatization markedly increased hemoglobin ( P < 0.001), hematocrit ( P < 0.001), and extracellular HSP72 ( P = 0.01). These data suggest that 10 days of normobaric hypoxic acclimatization combined with moderate-intensity exercise training improves V̇o2max in NOR and HE, but does not seem to affect exercise performance or thermoregulatory responses in any of the tested environmental conditions.

NEW & NOTEWORTHY The potential crossover effect of hypoxic acclimatization on performance in the heat remains unexplored. Here we show that 10-day continuous hypoxic acclimatization combined with moderate-intensity exercise training can increase maximal oxygen uptake in hot conditions.

Effects of 10 days of separate heat and hypoxic exposure on heat acclimation and temperate exercise performance

Adaptations to heat and hypoxia are typically studied in isolation but are often encountered in combination. Whether the adaptive response to multiple stressors affords the same response as when examined in isolation is unclear. We examined 1) the influence of overnight moderate normobaric hypoxia on the time course and magnitude of adaptation to daily heat exposure and 2) whether heat acclimation (HA) was ergogenic and whether this was influenced by an additional hypoxic stimulus. Eight males [V̇o2max = 58.5 (8.3) ml·kg−1·min−1] undertook two 11-day HA programs (balanced-crossover design), once with overnight normobaric hypoxia (HAHyp): 8 (1) h per night for 10 nights [[Formula: see text] = 0.156; SpO2 = 91 (2)%] and once without (HACon). Days 1, 6, and 11 were exercise-heat stress tests [HST (40°C, 50% relative humidity, RH)]; days 2–5 and 7–10 were isothermal strain [target rectal temperature (Tre) ~38.5°C], exercise-heat sessions. A graded exercise test and 30-min cycle trial were undertaken pre-, post-, and 14 days after HA in temperate normoxia (22°C, 55% RH; FIO2 = 0.209). HA was evident on day 6 (e.g., reduced Tre, mean skin temperature (T̄sk), heart rate, and sweat [Na+], P < 0.05) with additional adaptations on day 11 (further reduced T̄sk and heart rate). HA increased plasma volume [+5.9 (7.3)%] and erythropoietin concentration [+1.8 (2.4) mIU/ml]; total hemoglobin mass was unchanged. Peak power output [+12 (20) W], lactate threshold [+15 (18) W] and work done [+12 (20) kJ] increased following HA. The additional hypoxic stressor did not affect these adaptations. In conclusion, a separate moderate overnight normobaric hypoxic stimulus does not affect the time course or magnitude of HA. Performance may be improved in temperate normoxia following HA, but this is unaffected by an additional hypoxic stressor.

PlanHab: Hypoxia counteracts the erythropoietin suppression, but seems to exaggerate the plasma volume reduction induced by 3 weeks of bed rest

The study examined the distinct and synergistic effects of hypoxia and bed rest on the erythropoietin (EPO) concentration and relative changes in plasma volume (PV). Eleven healthy male lowlanders underwent three 21‐day confinement periods, in a counterbalanced order: (1) normoxic bed rest (NBR; P_IO₂: 133.1 ± 0.3 mmHg); (2) hypoxic bed rest (HBR; P_IO₂: 90.0 ± 0.4 mmHg, ambient simulated altitude of ~4000 m); and (3) hypoxic ambulation (HAMB; P_IO₂: 90.0 ± 0.4 mmHg). Blood samples were collected before, during (days 2, 5, 14, and 21) and 2 days after each confinement to determine EPO concentration. Qualitative differences in PV changes were also estimated by changes in hematocrit and hemoglobin concentration along with concomitant changes in plasma renin concentration. NBR caused an initial reduction in EPO by ~39% (P = 0.04). By contrast, HBR enhanced EPO (P = 0.001), but the increase was less than that induced by HAMB (P < 0.01). All three confinements caused a significant reduction in PV (P < 0.05), with a substantially greater drop in HBR than in the other conditions (P < 0.001). Thus, present results suggest that hypoxia prevents the EPO suppression, whereas it seems to exaggerate the PV reduction induced by bed rest.

Defining the “dose” of altitude training: how high to live for optimal sea level performance enhancement

Chronic living at altitudes of ∼2,500 m causes consistent hematological acclimatization in most, but not all, groups of athletes; however, responses of erythropoietin (EPO) and red cell mass to a given altitude show substantial individual variability. We hypothesized that athletes living at higher altitudes would experience greater improvements in sea level performance, secondary to greater hematological acclimatization, compared with athletes living at lower altitudes. After 4 wk of group sea level training and testing, 48 collegiate distance runners (32 men, 16 women) were randomly assigned to one of four living altitudes (1,780, 2,085, 2,454, or 2,800 m). All athletes trained together daily at a common altitude from 1,250–3,000 m following a modified live high-train low model. Subjects completed hematological, metabolic, and performance measures at sea level, before and after altitude training; EPO was assessed at various time points while at altitude. On return from altitude, 3,000-m time trial performance was significantly improved in groups living at the middle two altitudes (2,085 and 2,454 m), but not in groups living at 1,780 and 2,800 m. EPO was significantly higher in all groups at 24 and 48 h, but returned to sea level baseline after 72 h in the 1,780-m group. Erythrocyte volume was significantly higher within all groups after return from altitude and was not different between groups. These data suggest that, when completing a 4-wk altitude camp following the live high-train low model, there is a target altitude between 2,000 and 2,500 m that produces an optimal acclimatization response for sea level performance.

Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory

AIM

The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO).

METHODS

Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration.

RESULTS

The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P ≤ 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P ≤ 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P ≤ 0.05).

CONCLUSION

In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.

Epo production at altitude in elite endurance athletes is not associated with the sea level hypoxic ventilatory response

The level of circulating erythropoietin (EPO) in response to a fixed level of hypoxia shows substantial inter-individual variability, the source of which is undetermined. Arterial PO(2) at altitude is regulated in part by the hypoxic ventilatory response, which also shows a wide inter-individual variability. We asked if the ventilatory response to hypoxia is related to the magnitude of EPO release at moderate altitude. Twenty-six national class US distance runners (17 M, 9 F) participated in a test of isocapnic hypoxic ventilatory response (HVR) at sea level, 2-7 days prior to departure to altitude. EPO measures were obtained at sea level and after 20 h at 2500 m. HVR for all subjects was 0.21±0.16 L min⁻¹ %SaO₂⁻¹ (range 0.01-0.61 L min⁻¹ %SaO₂⁻¹), with no significant difference between men and women. EPO was significantly increased from pre-altitude (8.6±2.6 ng ml(-1), range 4.0-14.6 ng ml⁻¹) to acute altitude (16.6±4.4 ng ml⁻¹, range 5.0-27.0 ng ml⁻¹), an increase of 92.2±70.1%. There was no significant sex difference in the EPO increase. ΔEPO for all subjects was not correlated with HVR (r=-0.17). Similarly, a statistically or physiologically significant correlation was not present between ΔEPO and HVR within the group of men (r=-0.22) or women (r=-0.19). The variability in the acute EPO response to moderate altitude is not explained by differences in peripheral chemoresponsiveness in elite distance runners. These results suggest that factors acting downstream from the lung influence the magnitude of the acute EPO response to altitude.

Environmental influences on hypothalamic–pituitary–thyroid function and behavior in Antarctica

We examined the physiological and psychological status of men and women who spent the summer (n=100) and/or winter (n=85) seasons in Antarctica at McMurdo (latitude 78.48 S, elevation 12 m) and South Pole (latitude 90 S, elevation 3880 m) stations to determine whether there were any significant differences by severity of the stations' physical environment. Physiological measures (body mass index, blood pressure, heart rate, tympanic temperature), serum measures of thyroid hormones, cortisol, and lipids and plasma catecholamines were obtained at predeployment (Sep-Oct) and the beginning of the summer (November) and winter (Mar-Apr) seasons. Cognitive performance and mood were assessed using the Automatic Neuropsychological Assessment Metric - Isolated and Confined Environments (ANAM-ICE), a computerized test battery. South Pole residents had a lower body mass index (p<0.05) and body temperature (p<0.01) and higher levels of plasma norepinephrine (p<0.05) in summer and winter than McMurdo residents. Upon deployment from the United States and during the summer, South Pole residents experienced significantly higher thyroid hormone values (free and total T(3) and T(4)) (p<0.01) than McMurdo residents; in summer they also experienced lower levels of triglycerides (p<0.01) cortisol (p<0.05) and LDL (p<0.05). In winter, South Pole residents also experienced a 39% decrease in serum TSH compared with a 31.9% increase in McMurdo (p<0.05). South Pole residents also were significantly more accurate (p<0.05) and efficient (p<0.01) in performance of complex cognitive tasks in summer and winter. Higher thyroid hormone levels, combined with lower BMI and body temperature, may reflect increased metabolic and physiological responses to colder temperatures and/or higher altitude at South Pole with no apparent adverse effect on mood and cognition.

Erythropoietin regulations in humans under different environmental and experimental conditions

In the adult human, the kidney is the main organ for the production and release of erythropoietin (EPO). EPO is stimulating erythropoiesis by increasing the proliferation, differentiation and maturation of the erythroid precursors. In the last decades, enormous efforts were made in the purification, molecular encoding and description of the EPO gene. This led to an incredible increase in the understanding of the EPO-feedback-regulation loop at a molecular level, especially the oxygen-dependent EPO gene expression, a key function in the regulation loop. However, studies in humans at a systemic level are still very scanty. Therefore, it is the purpose of the present review to report on the main recent investigations on EPO production and release in humans under different environmental and experimental conditions, including: (i) studies on EPO circadian, monthly and even annual variations, (ii) studies in connection with short-, medium- and long-term exercise at sea-level which will be followed (iii) by studies performed at moderate and high altitude.

Timing the arrival at 2340 m altitude for aerobic performance

This study tested the hypothesis that maximal oxygen uptake (VO(2max)) and performance increase upon altitude acclimatization at moderate altitude. Eight elite cyclists were studied at sea level, and after 1 (Day 1), 7 (Day 7), 14 (Day 14) and 21 (Day 21) days of exposure to 2340 m. Capillary blood samples were taken on these days before performing two consecutive maximal exercise trials. Acclimatization increased hemoglobin concentration and arterial oxygen content. On Day 1, VO(2max) and time to exhaustion (at 80% of sea-level maximal power output) decreased by 12.8% (P<0.05) and 25.8% (P<0.05), respectively, compared with the corresponding sea-level values. Subsequently, these parameters increased by 3.2% (P<0.05) and 6.0% (P<0.05) from Days 1 to 7, by 4.8% (P<0.05) and 5.7% (P<0.05) from Days 7 to 14, followed by 0.7% (P>0.05) and 1.4% (P>0.05) from Days 14 to 21, respectively. These data suggest that endurance athletes competing at altitudes around 2340 m should expose themselves to this altitude at least 14 days before competition.

ACE gene polymorphism and erythropoietin in endurance athletes at moderate altitude

PURPOSE

To determine the role of the ACE (I/D) gene polymorphism on erythropoietic response in endurance athletes after natural exposure to moderate altitude.

METHODS

Erythropoietic activity was measured in 63 male endurance athletes following natural exposure to moderate altitude (2200 m) during 48 h. Erythropoietin (EPO) levels and hemoglobin (Hb) concentrations were measured at baseline and 12, 24, and 48 h after reaching the set altitude. Reticulocyte counts were determined at baseline and 48 h thereafter. Subjects were grouped into two groups (responders and nonresponders) based on significant increase in EPO levels (median: > 16.5 ng x m(-1)) after 24 h at altitude. ACE gene polymorphism was ascertained by polymerase chain reaction (DD, 31 (49%); ID, 24 (38%); II, 8 (13%)).

RESULTS

Overall, EPO levels significantly increased at 12 (70%; P = 0.0001) and 24 h (72%; P = 0.0001) above baseline concentration following exposure to 2200 m. Thereafter, EPO concentration decreased at 48 h, but a significant increase in Hb levels (4.6 +/- 4%; P = 0.0001) and reticulocyte count (50.5 +/- 79%; P = 0.0001) was observed at the end of the experiment, suggesting negative feedback. There were no significant differences in EPO and Hb concentration profiles between subjects with DD genotype and those with other genotypes (ID/II). Moreover, responders (N = 42; DD, 50%; ID/II, 50%) and nonresponders (N = 21; DD, 48%; ID/II, 52%) showed a similar erythropoietic profile during the experiment and the ACE gene polymorphism did not influence the time course of the erythropoietic response.

CONCLUSIONS

The ACE gene polymorphism does not influence erythropoietic activity in endurance athletes after short-term exposure to moderate altitude.

Austrian Moderate Altitude Study (AMAS 2000): Erythropoietic Activity and Hb–O2 Affinity During a 3-Week Hiking Holiday at Moderate Altitude in Persons with Metabolic Syndrome

Moderate altitude hypoxia (1500 to 2500 m) is known to stimulate erythropoiesis and to improve oxygen transport to tissue by a reduction of Hb-O(2) affinity. Whether this adaptation also occurs in tourists with metabolic syndrome has not yet been investigated sufficiently. Thus, we performed a prospective field study to measure erythropoietic parameters and oxygen transport properties in 24 male volunteers with metabolic syndrome during a 3- week holiday program at 1700 m consisting of four guided, individually adapted hiking tours per week. The following examinations were performed: baseline investigations at 500 m (T1); examinations at moderate altitude on day 1 (T2), day 4 (T3), day 9 (T4), and day 19 (T5); and postaltitude tests (T6) 7 to 10 days after return. On day 1 and day 19, a walk on a standardized hiking test route with oxygen saturation (SpO(2)) measure points was performed. Hemoglobin, packed cell volume, and red cell count showed changes over time, with higher values at T5 as compared to baseline. Reticulocyte count and erythropoietin (EPO) were increased at T2 and increased further until T5. EPO declined toward prealtitude values. P50-value (blood PO(2) at 50% hemoglobin oxygen saturation at actual pH) increased during the altitude sojourn (maximum increase at T5 by +0.40 kPa). At T5 all volunteers had a higher SpO(2) before, during, and at the end of the test route compared to T1. During adaptation to moderate altitude, persons with metabolic syndrome exhibit an increase in EPO and a rightward shift of the oxygen dissociation curve that is similar to healthy subjects.

Erythropoietin

This article summarizes recent advances in understanding the production and action of the hormone erythropoietin (Epo) with respect to high altitude physiology and sports medicine. Hypoxia is the main stimulus for Epo gene expression. An O2-labile protein (hypoxia-inducible factor 1, HIF-1) has been identified that is hydroxylated and degraded under normoxic conditions but active in hypoxia, where it enhances Epo gene transcription resulting in elevated hemoglobin levels and O2 capacity of the blood. The stimulation of Epo production at lowered arterial O2 tension can be maladaptive, if erythrocytosis develops such as seen in high altitude habitants. Within physiological limits the aerobic power increases in parallel with blood O2 capacity. Therefore, some elite athletes have misused recombinant human Epo (rhEpo), which is a beneficial anti-anemic drug in clinical practice. Indirect and direct methods to detect rhEpo doping have been recently developed.

Fine tuning the HIF-1 'global' O2 sensor for hypobaric hypoxia in Andean high-altitude natives

Included in the acute response of lowlanders exposed to reduced oxygen availability is an elevated red blood cell count due to increased erythropoietin (Epo) synthesis. According to current thinking, hypoxia is "sensed" by hydroxylases that permit Hypoxia Inducible Factor 1alpha (HIF-1alpha) to complex with HIF-1beta to form a transcriptional activator (HIF-1) that drives expression of hypoxia-sensitive genes (such as EPO) under hypoxic conditions. In altitude-adapted Andean natives, the Epo hypoxic response may be blunted; however, our data indicate that the DNA sequences of the genes encoding Epo (including the 3' regulatory region) and HIF-1alpha appear to be conserved. Hence, adaptive changes in the Andean hypoxic response are not a consequence of changes in the primary sequence of these proteins or of known transcriptional regulatory domains of EPO. These results suggest that the altered erthropoietic response in Andean natives reflects adaptations in hypoxia sensing, rather than hypoxia response, mechanisms.

Determinants of erythropoietin release in response to short-term hypobaric hypoxia

We measured blood erythropoietin (EPO) concentration, arterial O(2) saturation (Sa(O(2))), and urine PO(2) in 48 subjects (32 men and 16 women) at sea level and after 6 and 24 h at simulated altitudes of 1,780, 2,085, 2,454, and 2,800 m. Renal blood flow (Doppler) and Hb were determined at sea level and after 6 h at each altitude (n = 24) to calculate renal O(2) delivery. EPO increased significantly after 6 h at all altitudes and continued to increase after 24 h at 2,454 and 2,800 m, although not at 1,780 or 2,085 m. The increase in EPO varied markedly among individuals, ranging from -41 to 400% after 24 h at 2,800 m. Similar to EPO, urine PO(2) decreased after 6 h at all altitudes and returned to baseline by 24 h at the two lowest altitudes but remained decreased at the two highest altitudes. Urine PO(2) was closely related to EPO via a curvilinear relationship (r(2) = 0.99), although also with prominent individual variability. Renal blood flow remained unchanged at all altitudes. Sa(O(2)) decreased slightly after 6 h at the lowest altitudes but decreased more prominently at the highest altitudes. There were only modest, albeit statistically significant, relationships between EPO and Sa(O(2)) (r = 0.41, P < 0.05) and no significant relationship with renal O(2) delivery. These data suggest that 1) the altitude-induced increase in EPO is "dose" dependent: altitudes > or =2,100-2,500 m appear to be a threshold for stimulating sustained EPO release in most subjects; 2) short-term acclimatization may restore renal tissue oxygenation and restrain the rise in EPO at the lowest altitudes; and 3) there is marked individual variability in the erythropoietic response to altitude that is only partially explained by "upstream" physiological factors such as those reflecting O(2) delivery to EPO-producing tissues.

Erythropoiesis in women during 11 days at 4,300 m is not affected by menstrual cycle phase

Because the ovarian steroid hormones, progesterone and estrogen, have higher blood levels in the luteal (L) than in the follicular (F) phase of the menstrual cycle, and because of their known effects on ventilation and hematopoiesis, we hypothesized that less hypoxemia and less erythropoiesis would occur in the L than the F phase of the cycle after arrival at altitude. We examined erythropoiesis with menstrual cycle phase in 16 women (age 22.6 +/- 0.6 yr). At sea level, 11 of 16 women were studied during both menstrual cycle phases, and, where comparison within women was available, cycle phase did not alter erythropoietin (n = 5), reticulocyte count (n = 10), and red cell volume (n = 9). When all 16 women were taken for 11 days to 4,300-m altitude (barometric pressure = 462 mmHg), paired comparisons within women showed no differences in ovarian hormone concentrations at sea level vs. altitude on menstrual cycle day 3 or 10 for either the F (n = 11) or the L (n = 5) phase groups. Arterial oxygen saturation did not differ between the F and L groups at altitude. There were no differences by cycle phase on day 11 at 4,300 m for erythropoietin [22.9 +/- 4.7 (L) vs. 18.8 +/- 3.4 mU/ml (F)], percent reticulocytes [1.9 +/- 0.1 (L) vs. 2.1 +/- 0.3% (F)], hemoglobin [13.5 +/- 0.3 (L) vs. 13.7 +/- 0.3 g/100 ml (F)], percent hematocrit [40.6 +/- 1.4 (L) vs. 40.7 +/- 1.0% (F)], red cell volume [31.1 +/- 3.6 (L) vs. 33.0 +/- 1.6 ml/kg (F)], and blood ferritin [8.9 +/- 1.7 (L) vs. 10.2 +/- 0.9 microg/l (F)]. Blood level of erythropoietin was related (r = 0.77) to arterial oxygen saturation but not to the levels of progesterone or estradiol. We conclude that erythropoiesis was not altered by menstrual cycle phase during the first days at 4,300-m altitude.

Increase in immune activation, vascular endothelial growth factor and erythropoietin after an ultramarathon run at moderate altitude

The present study was performed to investigate the effects of exhaustive long lasting exercise at moderate altitude on the time course of serum immunomodulatory peptides, vascular endothelial growth factor (VEGF) and serum erythropoietin (EPO). Thirteen well trained runners participated at the Swiss Alpine Marathon of Davos (distance 67 km, altitude difference 2300 m). Interleukin-6 was significantly elevated in the first 2h after the run. In contrast, tumor necrosis factor-alpha and both soluble tumor necrosis factor-a receptors I and II were increased after exercise termination and showed sustained serum concentrations the following days. Neopterin, a serum marker for the activation of the cellular immune system, was increased until day two after the run. Immediately after the run VEGF was significantly elevated and further increased 2.4-fold until day five post exercise (p = 0.005). EPO was also increased after exercise but reached its maximum 2 h after the run (2-fold increase; p = 0.004) and decreased thereafter. The main findings of our study are that prolonged strenuous exercise at moderate altitude induced a significant long lasting increase in serum VEGF and EPO which was accompanied by an activation of the immune system.

Individual variation in response to altitude training

Moderate-altitude living (2,500 m), combined with low-altitude training (1,250 m) (i.e., live high-train low), results in a significantly greater improvement in maximal O2 uptake (V(02)max) and performance over equivalent sea-level training. Although the mean improvement in group response with this "high-low" training model is clear, the individual response displays a wide variability. To determine the factors that contribute to this variability, 39 collegiate runners (27 men, 12 women) were retrospectively divided into responders (n = 17) and nonresponders (n = 15) to altitude training on the basis of the change in sea-level 5,000-m run time determined before and after 28 days of living at moderate altitude and training at either low or moderate altitude. In addition, 22 elite runners were examined prospectively to confirm the significance of these factors in a separate population. In the retrospective analysis, responders displayed a significantly larger increase in erythropoietin (Epo) concentration after 30 h at altitude compared with nonresponders. After 14 days at altitude, Epo was still elevated in responders but was not significantly different from sea-level values in nonresponders. The Epo response led to a significant increase in total red cell volume and V(O2) max in responders; in contrast, nonresponders did not show a difference in total red cell volume or V(O2)max after altitude training. Nonresponders demonstrated a significant slowing of interval-training velocity at altitude and thus achieved a smaller O2 consumption during those intervals, compared with responders. The acute increases in Epo and V(O2)max were significantly higher in the prospective cohort of responders, compared with nonresponders, to altitude training. In conclusion, after a 28-day altitude training camp, a significant improvement in 5,000-m run performance is, in part, dependent on 1) living at a high enough altitude to achieve a large acute increase in Epo, sufficient to increase the total red cell volume and V(O2)max, and 2) training at a low enough altitude to maintain interval training velocity and O2 flux near sea-level values.

Increase in serum vascular endothelial growth factor levels during altitude training

The present study was performed to evaluate the effects of physical exercise at altitudes on serum vascular endothelial growth factor (VEGF) levels. Eight subjects underwent intensive swimming training for 21 days at 1886 m. After altitude training commenced, red blood cell (RBC) counts and erythropoietin levels increased, but both haemoglobin and haematocrit levels did not change significantly. The serum level of VEGF, measured by means of a highly sensitive chemiluminescence (ELISA), showed a transient decrease 10 days after start of the altitude training, thereafter increasing significantly to reach a peak level 19 days later, rising from 23.0 +/- 5.3 to 46.0 +/- 14.6 pg mL-1 (P < 0.05 vs. before). On return to low altitude in Japan, the level of VEGF decreased, and 1 month later had returned to initial levels. Endurance training at altitudes increases serum VEGF levels; this could be an adaptive reaction to hypoxic conditions. This result suggests that VEGF may provide a new physiological parameter for hypoxic stress imposed by high altitude training.

Application of a modified INCSTAR Epo-trac 125/RIA for measurement of serum erythropoietin concentration in elite athletes

OBJECTIVES

To evaluate the analytical performance of a radioimmunoassay for measurement of erythropoietin.

DESIGN AND METHODS

The INCSTAR Epo-trac 125I radioimmunoassay was examined for applications requiring sensitivity and precision within the normal range.

RESULTS

Sensitivity was improved by increasing sample volume to 300 microL. Minimal detectable concentration was determined at 5.3 U/L, %CV ranged from 4.8-5.8 and 13.3-6.4 for intra- and inter-assay imprecision, respectively. Accuracy was maximized by controlling for lipemic and hemolyzed samples and ensuring serum was separated from the clot within 1 h of collection. Values demonstrated good correlation to the Diagnostic Systems Laboratory RIA-kit.

CONCLUSIONS

With sample volume increased to 300 microL and control of sample preparation, the INCSTAR Epo-trac 125/RIA showed improved precision. Assay sensitivity at lower values allows resolution of changes in erythropoietin within the normal reference range. Age was not found to influence erythropoietin concentration. Within 10 days sojourn at moderate altitude an increase in circulating erythropoietin and reticulocytosis was observed in swimmers.